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101.
John W. Drazin James A. Wollmershauser Heonjune Ryou Mason A. Wolak Edward P. Gorzkowski 《Journal of the American Ceramic Society》2020,103(1):60-69
Pressureless sintering approaches provide a simple avenue to manufacture dense ceramic parts with minimal processing equipment, but current pressureless sintering techniques have yet to demonstrate capabilities of producing dense ceramics while maintaining sub-50 nm grain sizes. Nanocrystalline yttria stablized zirconia ceramics were process from 4 mol% yttria stablized zirconia (4YSZ) nanopowders with a crystallite size of 7.5 nm using dry cold isostatic pressing (CIP) where powders are dried immediately prior to green compact formation and CIP vacuum bagging. It is shown that CIP pressures >75 000 psi (517 MPa) effectively remove pores larger than 100 nm and that pressureless sintering occurs at reduced temperatures for green densities ≥50%. Though the sintering kinetics are shown to be similar to other zirconia nanopowder sintering studies, the small initial crystallize size and reduced sintering temperature allowed densities as high as 97.2%, while retaining a ceramic grain size at or below 40 nm. Produced nanocrystalline 4YSZ ceramics with a grain size of 30.3 nm and a density of 96.3% had Vicker's hardnesses as high as 14.2 GPa and Vicker's indentation fracture resistance of 3.43 MPa·, demonstrating that simple processing approaches can be refined to fabricate nanocrystalline ceramics while maintaining high hardness and indentation fracture resistance. 相似文献
102.
CORRELATION OF DIFFUSION COEFFICIENTS FOR LIQUIDS AND DENSE FLUIDS WITH TEMPERATURE AND PRESSURE 下载免费PDF全文
On the basis of the free volume theory and activation energy concept,a fundamental equation whichtakes into account the effects of temperature and pressure has been developed.By introducing differentexpressions for the free volume and activation energy,several equations for fluid diffusion coefficients were derivedaccordingly.With the van der Waals free volume and intermal energy formula,a three-parameter model for fluiddiffusion coeffficients at moderate pressure was obtained.The grand average absolute deviation percent of 345data points (44 systems)for self-and infinite dilute inter-diffusivities is 2.32,against the results of the model ofCohen and Turnbull,4.13.In particular,by means of the modified Carnahan-Starling free volume equation,afour-parameter model with average abosolute deviation percent 2.64(30 systems,644 data points)for theestimation of dense fluid inter-and self-diffusivities at high pressures and in supercritical conditions was derived.The derived model is superior to the method of L 相似文献
103.
Software systems can be represented as complex networks and their artificial nature can be investigated with approaches developed in network analysis.Influence maximization has been successfully applied on software networks to identify the important nodes that have the maximum influence on the other parts.However,research is open to study the effects of network fabric on the influence behavior of the highly influential nodes.In this paper,we construct class dependence graph(CDG)networks based on eight practical Java software systems,and apply the procedure of influence maximization to study empirically the correlations between the characteristics of maximum influence and the degree distributions in the software networks.We demonstrate that the artificial nature of CDG networks is reflected partly from the scale free behavior:the in-degree distribution follows power law,and the out-degree distribution is lognormal.For the influence behavior,the expected influence spread of the maximum influence set identified by the greedy method correlates significantly with the degree distributions.In addition,the identified influence set contains influential classes that are complex in both the number of methods and the lines of code(LOC).For the applications in software engineering,the results provide possibilities of new approaches in designing optimization procedures of software systems. 相似文献
104.
Efficient and selective oxidation of primary and secondary alcohols to the corresponding aldehydes and ketones catalyzed by potassium permanganate supported on Kieselguhr reagent under solvent free conditions are reported. 相似文献
105.
以麦芽酚或乙基麦芽酚为起始原料,经乙酰化、钯碳氢化、羰基α位乙酰氧化和脱乙酰基等4步反应,合成了两种双羟基吡喃酮化合物。利用核磁共振氢谱、碳谱和高分辨质谱对每一步反应产物进了结构表征,优化了合成反应工艺,并通过清除自由基反应对化合物的抗氧化活性进行了测试。结果表明,双羟基吡喃酮化合物对ABTS+?、DPPH?和galvinoxyl?三种自由基清除率分别达到88.9%、83.8%和68.4%,明显高于维生素E和2,6-二叔丁基对甲酚的自由基清除率,表现出优异的抗氧化活性。构效关系研究表明,在吡喃酮结构中引入羟基或增强侧链取代基的给电子能力均能提高化合物清除自由基的能力,为新型抗氧化剂的合成开发提供了参考。 相似文献
106.
Induction of systemic resistance to feeding of beet armyworm, Spodoptera exigua, was investigated in two isogenic lines of Stoneville 213 cotton, Gossypium hirsutum, that differed in the presence of pigment glands. In laboratory bioassays, larvae strongly preferred to feed on glandless cotton plants when presented a choice between undamaged terminal leaves of undamaged glanded and glandless plants. Feeding damage inflicted by S. exigua larvae on the two oldest leaves of glanded plants seven days prior to feeding bioassays caused larvae to prefer by 33-fold the undamaged terminal foliage from undamaged plants compared to that from damaged plants. Feeding damage on glandless plants caused only a 2.6-fold greater preference for terminal foliage from undamaged plants over foliage from previously damaged plants. Extracts of terminal foliage from glanded cotton damaged seven days earlier had significantly greater quantities of terpenoid aldehydes (hemigossypolone, gossypol, and heliocides) than did foliage from undamaged glanded plants. Terpenoid aldehydes were undetectable in extracts of both undamaged and previously damaged glandless plants. The profile of volatile compounds collected from the headspace of mechanically damaged terminal leaves of undamaged glanded and glandless plants differed. Both cotton isolines released large quantities of lipoxygenase products (hexenyl alcohols, acetates, and butyrates), but glandless plants released only small amounts of mono- and sesquiterpenes compared to glanded plants. Glandless plants damaged seven days prior to volatile collection released significantly greater quantities of lipoxygenase products, -ocimene, and - and -farnesene than did undamaged glandless plants. Previously damaged glanded plants released significantly greater quantities of all mono- and sesquiterpenes and hexenyl acetates and butyrates, but not alcohols. The relative importance of volatile compounds versus terpenoid aldehydes in induced feeding deterrence in cotton to S. exigua larvae is still unclear. 相似文献
107.
Yuen May Choo Ah Ngan Ma Hawari Yahaya Y. Yamauchi M. Bounoshita M. Saito 《Journal of the American Oil Chemists' Society》1996,73(4):523-525
Successful separation of triglycerides, diglycerides, free fatty acids, carotenes, tocopherol, and tocotrienols from crude
palm oil has been achieved by supercritical fluid chromatography (SFC) with a combination of a C18 and a silica gel column.
The separation was carried out by the programmed extraction elution method. Free fatty acids were separated into five components
by gas-liquid chromatography; tocopherol and tocotrienols were also separated into four components by SFC analysis, and the
pure fractionated carotenes were obtained by preparative SFC. Thus, by using supercritical fluid chromatography, crude palm
oil components can be separated and fractionated, based on differences in their functional groups. 相似文献
108.
在水力机械等淹没水中设备的运行中,常遇到剧烈振动造成设备损坏等故障,多认为由共振引起。本文首先对单自由度简谐振动系统自由振动、强迫振动方程的稳态振动解进行无量纲化处理,计算出不同阻尼比条件下的共振频率比、共振幅值比,发现阻尼比、共振频率比、共振幅值比三者之间存在一一对应的单调变化关系,并据此提出了分别测量设备在水中及空气中的自由振动频率,假定空气中自由振动频率为设备固有频率,再依次确定水中阻尼比和共振幅值比的反求式估算方法。本研究采用敲击法进行了混流式水轮机模型转轮水中及空气中自由振动频率测试,发现其水中自由振动频率比空气中低,其水中一阶自由振动频率与空气中一阶自由振动频率之比约为0.758~0.872;如假定该值为水中自由振动频率比,可计算出相应的水中阻尼比为0.652~0.490,共振幅值比约为1.01~1.17。本研究还进行了中间固定两侧悬臂梁在空气及水中的真实共振试验,在两侧悬臂梁计算固有频率附近均发生明显共振,发现水中共振频率比空气中明显降低,用反求法获得的水中共振幅值比小于2,水中共振幅值对空气中初始振动幅值放大倍数也非常小,进一步说明水中共振时对激振幅值的放大作用非常有限。 相似文献
109.
目前几乎所有最先进的目标检测方法都依赖于预先定义的anchor,但是由于anchor的存在,网络会增加与anchor相关的计算开销,而且在现实世界中,目标尺度多种多样,比如地对空拍摄的无人机目标,预先定义的anchor不可能穷举所有的无人机尺度。因此,该文抛弃预先定义的anchor,采用anchor free的方法来检测无人机。该anchor free方法以目标中心区域的像素为训练样本来逐像素预测边界框的偏移量。针对地对空拍摄的无人机目标大部分都是小尺度的情况,采用高分辨率网络HRNet作为主干网络来提取小目标细粒度的特征,从而提高小目标检测的精度。相对于基于anchor的目标检测方法,该网络框架简单、灵活,并且可以自适应地预测无人机目标的边界框。在自己设计的无人机数据集上,该方法获得了更高的召回率和精确率。 相似文献
110.